Funny you ask... you know what really puzzles me ? I bet that at times, they use/try what Marshall offered them. I know they had a "thing" with Marshall, the Marshall 2000 (an extinct species now) was develop with the help of the band (look at Doyle book), so when the Young brothers say that they "dont like those new master volume amp Marshall made", they maybe were talking about the experience they had with it, not only what they heard.
If this is true, then, yes, it's more then a probability that they used them.
And, lastly, in the back of my mind, it may be that in the end, they dont really gives a sh*t about the amps, they just plug them and use them. This kind of "I dont care and if you dont like it, then f*ck it" couldn't be more representative of the Young brothers! This kind of "I take no prisonner" approach is why we so much love these guys!
And just think about Slash and his S.I.R. amp. All that time he tought that it was a JCM 800, when in fact it was a Super lead. The tech in the interview say to Slash "See, it has 4 holes, so it's a Superlead model, a 1959 moded with a master volume" to which Slash respond "Hey, I havent noticed that!" I goes to say that these guitar heroes are what they are, guitar player extraodinaire that dont fuss with details (unlike me lol).
I saw a recent pick of the Young brothers in front of a "Ard" amp (I guess Wizard, pround Canadian amp maker woohoo!!!... see the pic here http://www.wizardamplification.com/artists.htm
) I know the pic isn't "vintage", i think it's taken from the BlackIce sessions, but it means that they aren't "stuck" in a mold they feel they should hold on to. So, yes, 2203/2204 was maybe the tone of the BIB album. I guess that in 1980, that 2203/2204 was a big thing and they gave it a try!
And lastly, when I hear you play, I bet that even if YOU play on a lousy Line6 15 watt solidstate amp, YOU'd make it sound like Angus, cause you have it in your fingers! Now... *I*
have to use all the techno I can get to approximate that sound... did I told you my superlead is coming ?
Take care bro!